An example of a known louvered exhaust nozzle is described in UK Patent GB 1018581. In this disclosure a nozzle outlet for a gas turbine engine comprises a plurality of adjacent vanes which are each pivotally mounted to a support for spanwise rotation. The vanes are linked together for coordinated pivotal movement by means of a rigid connecting rod. Collectively the vanes, support and connecting rod define a parallelogram linkage. In use the thrust produced by the nozzle can be directed in selective predetermined directions by rotating the vanes.
Louvered exhaust nozzles offer many advantages over conventional vectorable nozzles, particularly for aircraft which utilize lift fans for vertical thrust. In these applications it is necessary for the lift units and associated vectorable nozzles to be located within the aircraft structure. With conventional vectorable nozzles it is not always possible to achieve this requirement without first compromising airframe design in accordance with nozzle stowability. This problem does not arise with the inherently compact louvered exhaust nozzle, which, during periods of non use, may be stowed in a relatively tight envelope simply by rotating the nozzle vanes flush with the aircraft fuselage.
A major problem associated with prior art louvered exhaust nozzles resides in the nozzle's ability to provide satisfactory performance over a wide vectoring range. This problem arises because in the parallelogram type arrangement described the vanes are constrained to rotate by equal amounts throughout the nozzle vectoring range. This causes the combined nozzle throat area to vary as the vanes rotate, resulting in problems associated with area mismatching. It is well understood that these problems can be overcome by providing each of the vanes with its own separate actuator so that the vanes may be rescheduled by different amounts in a manner which avoids area variation. Unfortunately this is not a practical solution for aircraft powerplant applications as any benefit derived would be negated by the increased weight and complexity of the nozzle actuation system.